Separating 1,1,1,3,3-pentafluoropropane from hydrogen fluoride

ABSTRACT

Disclosed are processes for separating 1,1,1,3,3-pentafluoropropane (HFC-245fa) from hydrogen fluoride (HF) by distillation, wherein hydrocarbons, chloroflurocarbons, hydrochlorofluorocarbons and fluorocarbons are used as entraining agents. The processes comprise: contacting a first mixture comprising HFC-245fa and HF with an entraining agent selected from the group consisting of hydrocarbons, chlorofluorocarbons, hydrochlorofluorocarbons and fluorocarbons to form a second mixture, distilling the second mixture and thereby separating the HFC-245fa from HF and entraining agent, and recovering HFC-245fa substantially-free of HF.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/US98/214499 filed Oct. 16, 1998 whichclaims the priority benefit of U.S. Provisional Application No.60/062277, filed Oct. 17, 1997.

FIELD OF THE INVENTION

The present invention relates to processes for separating1,1,1,3,3-pentafluoropropane (HFC-245fa) from hydrogen fluoride (HF) bydistillation, wherein hydrocarbons, chlorofluorocarbons,hydrochlorofluorocarbons and fluorocarbons are used as entrainingagents.

BACKGROUND OF THE INVENTION

New regulations have been established to protect the stratospheric ozonelayer from possible damage by chlorofluorocarbons (CFCs).1,1,1,3,3-Pentafluoropropane (CF₃CH₂CHF₂, HFC-245fa ) is ahydrofluorocarbon (HFC) which may be used either alone or in blends withother materials as a non-ozone depleting replacement for CFCs. HFC-245famay be prepared by fluorinating appropriate halopropanes or propeneswith hydrogen fluoride (HF). For example, HFC-245fa may be prepared byfluorinating 1-chloro-3,3,3-trifluoropropene in the presence of antimonypentachloride catalyst as is described in U.S. Pat. No. 5,616,819. TheHFC-245fa product may contain a variety of impurities such as by-producthydrogen chloride (HCl) and fluorocarbon by-products, as well asunreacted chlorinated precursors and hydrogen fluoride (HF). Thepresence of HF in HFC-245fa product is objectionable for most uses ofHFC-245fa. While most of these impurities can be removed from HFC-245faby conventional distillation, HF is difficult to remove by conventionaldistillation because HF and HFC-245fa form an azeotrope. This azeotropeis disclosed in World Intellectual Property Organization publication WO97/5,089. Due to the formation of the HF/HFC-245fa azeotrope, it isdifficult, if not impossible, to completely separate HFC-245fa and HF byconventional distillation to produce streams of HFC-245fa or HF that aresubstantially-free of the other compound.

The use of conventional methods for removing the HF, such as scrubbingthe HFC-245fa with water or in water/caustic solutions, causes loss ofthe utility of the HF for further reaction and incurs significantproduct loss due to the high solubility of HFC-245fa in water.

Where many organic compounds form an azeotrope with HF, it is sometimespossible to effect a phase separation by condensing and cooling themixture, wherein the mixture separates into two liquid phases, onecomprising increased HF concentration and the other comprising increasedorganic concentration relative to the HF and organic concentrations inthe azeotrope. Such methods typically do not produce substantially-purefractions of either HF or organic. Further, mixtures of HF and HFC-245fado not exhibit such phase separation even when cooled below −25° C.

World Intellectual Property Organization publication WO 97/05089discloses azeotropic distillation processes for separating HFC-245fa andHF. To obtain high purities and high-recovery-efficiencies of HFC-245faand HF, these methods require distillating the HFC-245fa andHF-containing streams successively at divergent pressures, which isextremely expensive in practice. It is difficult to obtain HFC-245faand/or HF substantially-free of the other component by such a method.

SUMMARY OF THE INVENTION

The present invention comprises processes for separating1,1,1,3,3-pentafluoropropane (HFC-245fa) from hydrogen fluoride (HF),comprising:

contacting a first mixture comprising 1,1,1,3,3-pentafluoropropane(HFC-245fa) and hydrogen fluoride (HF) with an entraining agent to forma second mixture,

distilling the second mixture and thereby separating the1,1,1,3,3-pentafluoropropane (HFC-245fa) from hydrogen fluoride (HF) andentraining agent, and

recovering 1,1,1,3,3-pentafluoropropane (HFC-245fa).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a distillation system that can be usedfor practicing an aspect of the inventive process.

FIG. 2 is a schematic diagram of a distillation system that can be usedfor practicing an aspect of the inventive process.

FIG. 3 is a schematic diagram of a distillation system that can be usedfor practicing an aspect of the inventive process.

FIG. 4 is a graphical representation at +20° C. of an azeotropic andazeotrope-like composition formed between HF and HFC-245fa.

FIG. 5 is a graphical representation at +40° C. of an azeotropic andazeotrope-like composition formed between HF and HCFC-124.

FIG. 6 is a graphical representation at about −20° C. of an azeotropicand azeotrope-like composition formed between HF and CFC-114.

FIG. 7 is a graphical representation at about +20° C. of an azeotropicand azeotrope-like composition formed between HF and CFC-114a.

FIG. 8 is a graphical representation at about −20° C. of an azeotropicand azeotrope-like composition formed between HF and CFC-115.

FIG. 9 is a graphical representation at about +30° C. of an azeotropicand azeotrope-like composition formed between HF and HCFC-142b.

DETAILED DESCRIPTION

The present inventors have found that HFC-245fa may be separated from HFsuch that either HFC-245fa or HF may be recovered substantially-free ofthe other, such that high-recovery-efficiency of each is obtained, andsuch that the separation is effected in an economical manner, bydistilling a mixture comprising HF and HFC-245fa in the presence of anentraining agent that interacts in a non-ideal manner with the mixture.The entraining agents of the present invention increase the volatilityof HF relative to HFC-245fa thus allowing the HFC-245fa to be separatedfrom HF by distillation.

HFC-245fa and HF in their separated and generally pure states haveatmospheric pressure boiling points of about +14° C. and +19° C.,respectively. However, a mixture comprising HFC-245fa and HF exhibitsnon-ideal behavior such that the relative volatility of HFC-245fa to HFbecomes 1.0 at specific concentrations of HFC-245fa and HF and specificpressures and temperatures, which indicates the formation of anazeotropic or azeotrope-like composition. The formation of an azeotropeor azeotrope-like composition comprising HF and HFC-245fa makesseparation by conventional distillation ineffective in simultaneouslyrecovering HFC-245fa product that is substantially-free of HF andobtaining high-recovery-efficiency of the HFC-245fa product. Byconventional distillation is meant that only the relative volatility ofthe components of the mixture to be separated are used to separate thecomponents.

To determine the relative volatility of HF and HFC-245fa, a method knownas the “PTx Method” was used. Use of the PTx Method is described indetail in “Phase Equilibrium in Process Design”, Wiley-IntersciencePublisher, 1970, written by Harold R. Null, on pages 124 to 126; herebyincorporated by reference. In the PTx method, the total absolutepressure in a cell of known volume is measured at a constant temperaturefor various known binary compositions of HFC-245fa and HF. These totalpressure measurements are converted into equilibrium vapor and liquidcompositions in the PTx cell by using an activity coefficient equationmodel such as the Non-Random, Two-Liquid (NRTL) equation, whichrepresents liquid phase nonidealities. Use of an activity coefficientequation such as the NRTL equation is described in greater detail in“The Properties of Gases and Liquids,” 4^(th) edition, published byMcGraw Hill, written by Reid, Prausnitz and Poling, on pages 241 to 387,and in “Phase Equilibria in Chemical Engineering,” published byButterworth Publishers, 1985, written by Stanley M. Walas, pages 165 to244. Both aforementioned references are hereby incorporated byreference.

The behavior of HF in such systems may also be calculated by using anappropriate HF association model in conjunction with the aforementionedmethods, such as described by W. Schotte, Ind.Eng.Chem.Process Des.Dev.1980, pp. 432-439; the disclosure of which is hereby incorporated byreference.

Without wishing to be bound by theory, it is believed that the NRTLequation can sufficiently predict whether or not HFC-245fa and HF and/orthe following other mixtures behave in an ideal manner, and cansufficiently predict the relative volatilities of the components in suchmixtures.

The problems associated with conventional distillation can be solved bythe present distillation process using entraining agents. The presentprocess may be employed when the components of the mixture have relativevolatilities that are insufficient to permit effective separation of thecomponents by conventional distillation In distillation using entrainingagents, an entraining agent is employed which causes the relativevolatilities of the components in the starting mixture to be alteredsuch that the relative volatility becomes sufficient to permitseparation of the components by distillation. The difficulty in applyingthis method is that there is no known way of predicting which if anycompound will be an effective entraining agent.

The results of PTx measurements and the above calculations indicate thatthe relative volatilities of HF and HFC-245fa are equal to 1.0 forcompositions of HF and HFC-245fa over a range of temperatures. Relativevolatilities of 1.0 in a mixture indicate the formation of an azeotrope.The results of PTx measurements and the above calculations indicate thatthe composition of the azeotropes varies with temperature.

By azeotropic or an azeotrope composition is meant a constant-boilingmixture of two or more substances that behaves as a single substance.One way to characterize an azeotropic composition is that the vaporproduced by partial evaporation or distillation of the liquid has thesame composition as the liquid from which it is evaporated or distilled,i.e., the mixture distills and refluxes without compositional change.Constant-boiling compositions are characterized as azeotropic becausethey exhibit either a maximum or minimum boiling point, relative to thatof the pure components. Azeotropic compositions are also characterizedby a minimum or a maximum in the vapor pressure measurements of themixture relative to the vapor pressure of the neat components as afunction of composition at a constant temperature.

It is also possible to characterize an azeotropic or azeotrope-likecomposition as a substantially constant-boiling admixture which mayappear under many guises, depending upon the conditions chosen, byseveral criteria:

The composition can be defined as an azeotrope of HF and anothercompound because the term “azeotrope” is at once both definitive andlimitative, and requires effective amounts of HF and the other compoundfor this unique composition of matter which can be a constant-boilingcomposition.

It is well known by those skilled in the art, that, at differentpressures, the composition of a given azeotrope will vary at least tosome degree, as will the boiling point temperature. Thus, an azeotropicor azeotrope-like composition of HF and another compound represents aunique type of relationship but with a variable composition whichdepends on temperature and/or pressure. Therefore, compositional ranges,rather than fixed compositions, are often used to define azeotropes.

An azeotrope or azeotrope-like composition of HF and another compoundcan be characterized by defining the compositions as an azeotropecharacterized by a boiling point at a given pressure, thus givingidentifying characteristics without unduly limiting the scope of theinvention by a specific numerical composition, which is limited by andis only accurate as the analytical equipment available.

It is recognized in the art that both the boiling point and the weight(or mole) percentages of each component of the azeotropic compositionmay change when the azeotrope or azeotrope-like liquid composition issubjected to boiling at different pressures. Thus, an azeotropic or anazeotrope-like composition may be defined in terms of the uniquerelationship that exists among components or in terms of the exactweight (or mole) percentages of each component of the compositioncharacterized by a fixed boiling point at a specific pressure.

By azeotrope-like is meant a composition that has a constant-boilingcharacteristic or a tendency not to fractionate upon boiling orevaporation. The composition of the vapor formed is the same as, orsubstantially the same as, the original liquid composition. Duringboiling or evaporation, the liquid composition, if it changes at all,changes only to a minimal or negligible extent. An azeotrope-likecomposition can also be characterized by the area that is adjacent tothe maximum or minimum vapor pressure in a plot of composition versusvapor pressure at a given temperature for components in the composition.Herein, a composition is azeotrope-like if, after about 50 weightpercent of the composition is removed such as by evaporation or boilingoff, the difference between the original composition and the compositionremaining is less than about 6 weight %, and normally less than about 3weight %, relative to the original composition.

It is also recognized in the art that when the relative volatility ofthe components in a mixture, e.g. HF and at least one other compound,approaches 1.0, such defines the mixture as forming an azeotrope-likecomposition. When the relative volatility is 1.0, such defines themixture as forming an azeotrope.

By low-boiling-azeotrope is meant that an azeotropic or azeotrope-likecomposition boils at a lower temperature at any given pressure than anyone of the components that comprise it would separately boil at thatpressure. Alternately, by low-boiling azeotrope is meant any azeotropicor azeotrope-like composition that has a higher vapor pressure at anygiven temperature than the vapor pressure of any one of the componentsthat comprise the azeotrope would separately have at that temperature.

The problems encountered upon conventional distillation of HF/HFC-245fa,such as the need for taller columns, higher energy input, and lowerresultant HFC-245fa recovery, can be solved by practicing the presentdistillation process. This distillation process is used as HF andHFC-245fa have a relative volatility that is insufficient to permiteffective separation by conventional distillation.

The present inventors have found that the relative volatility ofcompositions comprising HF and HFC-245fa can be altered from 1.0 in thepresence of entraining agents selected from: hydrocarbons,chlorofluorocarbons, hydrochlorofluorocarbons and fluorocarbons. Byentraining agent is meant any agent that, when added to a first mixture,interacts with at least one component in the first mixture to change therelative volatility of the components such that the components may beseparated by distillation. Preferably, entraining agents of the presentprocess comprise hydrocarbons, chlorofluorocarbons,hydrochlorofluorocarbons and fluorocarbons having a normal boiling pointgreater than about −50° C. and less than about 10° C. Preferredentraining agents of the present process arechloro-1,1,1,2-tetrafluoroethane (HCFC-124),chloro-1,1,2,2-tetrafluoroethane (HCFC-124a),dichloro-1,1,2,2-tetrafluoroethane (CFC-114),dichloro-1,1,1,2-tetrafluoroethane (CFC-114a),1-chloro-1,1-difluoroethane (HCFC-142b), chloropentafluoroethane(CFC-115), and propane.

In one embodiment of the present invention, entraining agent is added toa first mixture comprising HF and HFC-245fa to form a second mixturecomprising entraining agent, HF, and HFC-245fa. In the presence of theentraining agent, the relative volatility of the HF and HFC-245fa isincreased, with the HF becoming more volatile, thus permitting HF to beremoved as a distillation column overhead stream. This second mixture isdistilled under conditions such that a third mixture is formedcomprising a low-boiling azeotrope comprising entraining agent and HF.By distilling the second mixture under conditions such that alow-boiling HF/entraining agent azeotrope is formed, the HF may beseparated from the HFC-245fa by distilling the HF/entraining agentazeotrope third mixture overhead as a distillate stream, and recoveringas a distillation column bottoms stream the HFC-245fa that was presentin the first mixture, with the HFC-245fa recovered withhigh-recovery-efficiency and substantially-free of HF.

By substantially-free is meant that the residual HF in the HFC-245faproduct is less than 1 parts-per-million-by-weight (ppmw), preferrablyless than 100 parts-per-billion-by-weight (ppbw).

By high-recovery-efficiency is meant that greater than 95 weight %,preferably greater than 99 weight % of the HFC-245fa in the initialHFC-245fa-containing mixture is recovered as HFC-245fasubstantially-free of HF.

In a further embodiment of the present process, cooling the condensedHF/entraining agent azeotropic or azeotrope-like third mixture resultsin phase separation of the third mixture into two liquid phases. One ofthese phases is HF-enriched and the other phase is entrainingagent-enriched, both enriched relative to the HF and entraining agentconcentrations in the third mixture. The entraining agent-enriched layerobtained from this cooling step may be fed back to the distillation stepcarried out on the second mixture without further processing, or it canoptionally be distilled under conditions such that any HF remaining inthe entraining agent-enriched phase forms a low-boiling azeotropic orazeotrope-like composition with the entraining agent, where theHF/entraining agent azeotropic or azeotrope-like composition isdistilled overhead leaving an entraining agent productsubstantially-free of HF to exit the column bottoms. This HF/entrainingagent distillate may optionally be further separated by again feeding itto the aforementioned cooling step.

The HF-enriched layer from the cooling step may be used without furtherprocessing or, where further separation and purification of either theBF or entraining agent is desirable, it may optionally be distilledunder conditions that form a low-boiling HF/entraining agent azeotropicor azeotrope-like composition, recovering the HF/entraining agentazeotropic or azeotrope-like composition overhead as distillate, andrecovering HF substantially-free of entraining agent from the columnbottoms. The HF obtained from this step may be recycled back to areaction step to produce the HFC-245fa or used for other purposes. TheHF/entraining agent azeotropic of azeotrope-like composition distillatemay be further separated by again feeding it to the cooling step.

The present invention thus comprises a process for separating HF fromHFC-245fa comprising the steps of:

(1) contacting a first mixture comprising 1,1,1,3,3-pentafluoropropane(HFC-245fa) and hydrogen fluoride (HF) with an effective amount ofentraining agent selected from the group consisting of hydrocarbons,chlorofluorocarbons, and hydrochlorofluorocarbons to form a secondmixture,

(2) distilling the second mixture and thereby separating the1,1,1,3,3-pentafluoropropane (HC-245fa) from hydrogen fluoride (HF) andentraining agent,

(3) recovering 1,1,1,3,3-pentafluoropropane (HFC-245fa) as adistillation column bottom stream,

(4) recovering an azeotropic or azeotrope-like third mixture comprisingHF and entraining agent as a distillation column overhead stream fromsaid distilling step,

(5) optionally cooling and thereby phase-separating the condensed thirdmixture into a fourth mixture comprising an HF-enriched phase and afifth mixture comprising an entraining agent enriched phase,

(6) optionally distilling the fourth and/or fifth mixtures underconditions sufficient to form an azeotrope or azeotrope-like sixthmixture comprising HF and entraining agent as distillation columnoverhead stream

(7) optionally recovering a seventh mixture comprising HF or entrainingagent as a distillation column bottom stream from said distilling stepof the fourth and/or fifth mixtures,

(8) optionally recycling the sixth mixture to said cooling step, and

(9) optionally recycling the seventh mixture to said distilling step ofthe fourth and/or fifth mixtures.

By effective amount of entraining agent is meant an amount of at leastone entraining agent, which in the presence of HF and HFC-245fa, eitherresults in the formation of a lower-boiling azeotropic or azeotrope-likecomposition comprising HF and entraining agent or otherwise causes thevolatility of the HF to increase relative to the HFC-245fa. Thisdefinition includes amounts of each component which may vary dependingon the pressure applied to the composition so long as the azeotrope orazeotrope-like compositions continue to exist at the differentpressures, but with possible different boiling point temperatures.Effective amount also includes the amounts, such as may be expressed inweight percentages or mole percentages, of each component of thecompositions of the instant invention which form azeotropic orazeotrope-like compositions at temperature or pressures other than asdescribed herein. An effective amount of the entraining agent dependsupon the ratio of the HF to the entraining agent in the HF/entrainingagent azeotrope thus formed. Useful in the present process arecompositions of effective amounts of HFC-245fa and HF, HCFC-124 and HF,HCFC-124a and HF, HCFC-142b and HF, CFC-114 and HF, CFC-114a and HF,CFC-115 and HF, and propane and HF such that after about 50 weight % ofan original composition is evaporated or boiled off to produce theremaining composition, the difference between the original compositionand the remaining composition is typically about 6 weight percent orless, and normally 3 weight percent or less.

The entraining agents used in the present invention are generallycommercially available. If desired, the entraining agents may besubsequently removed from the HF by a variety of methods. A preferredmethod is to condense and cool the distillate from the firstdistillation comprising the HF/entraining agent azeotrope. Withcondensing and cooling the HF/entraining agent distillate, the mixtureseparates into two liquid layers, one HF-rich relative to theHF/entraining agent azeotrope composition, the other entrainingagent-rich relative to the azeotrope composition.

The entraining agent-rich layer may then be recycled to the HFC-245fa/HFseparation column for reuse, or if a stream substantially free of HF orcomplete separation of the HF is desired, this organic phase may be fedto a distillation column operated at a pressure and temperature thatcauses an azeotropic or azeotrope-like composition to form, composed ofHF and the entraining agent. Since the entraining agent is now in excessof the azeotropic composition, the HF may be removed from that excessentraining agent by distilling the HF/entraining agent azeotropeoverhead, with entraining agent substantially free of HF removed asbottoms from the column. By recycling the HF/entraining agent azeotropedistilled overhead from this column back to the decanter, essentiallyall of the entraining agent may be recovered as entraining agentsubstantially free of HF.

Similarly, the HF-rich layer from the cooling/decantation step may thenbe recycled back to the reaction step, or, if a HF stream substantiallyfree of entraining agent is desired, this HF phase may be fed to adistillation column operated at a pressure and temperature that causesan azeotropic or azeotrope-like composition to form comprising HF andthe entraining agent. Since the HF is now in excess of the azeotropiccomposition, the entraining agent may be removed from that excess HF bydistilling the HF/entraining agent azeotrope overhead, with HFsubstantially free of organic removed as bottoms from the column. Byrecycling the HF/organic azeotrope overhead from this column back to thecooler/decanter, essentially all of the HF may be recovered as pureproduct.

The specific conditions that can be used for practicing the inventiondepend upon a number of interrelated design parameters such as thediameter of the column, selected feed points, the number of separationstages in the column, among other parameters. The temperature and heattransfer area of the overhead condenser is normally sufficient tosubstantially fully condense the overhead product, or is optionallysufficient to achieve the desired reflux ratio by partial condensation.

The temperature that is employed at a given step in the inventiveprocess is a function of the pressure and design characteristics of thedistillation column, e.g., the ratio of entraining agent to the firstmixture.

Certain aspects of the invention can be better understood by referenceto FIG. 1. FIG. 1 schematically illustrates a system which can be usedto perform one aspect of the inventive distillation process. A firstmixture comprising HFC-245fa and HF is supplied via conduit 1 todistillation column 2. At least one liquid entraining agent is suppliedvia conduit 3 to distillation column 2. The entraining agent mayalternately be mixed in with the HFC-245fa and HF containing mixtureprior to the distillation column and simultaneously fed in via conduit1. Material comprising HFC-245fa substantially free of HF is removedfrom the column 1 bottoms via conduit 4. Material comprising theEntraining Agent and HF is removed from the column 2 as distillate viaconduit 5 and transported to condenser 6. A fraction of the distillateis then returned to column 2 as reflux via conduit 7, while theremainder is transported via conduit 8 to cooler 9 and from there to thedecanter 10. The material entering the decanter separates into twoliquid layers, one liquid layer entraining agent-rich layer, e.g., 11,the other liquid layer HF-rich, e.g., 12 on the top. The entrainingagent-rich layer is transported back to column 2 via conduit 13. TheHF-rich layer is transported to column 14 via conduit 15. Materialcomprising HF substantially free of entraining agent is removed fromcolumn 14 via conduit 16. Material comprising the entraining agent andHF is removed from the column 14 as distillate via conduit 17 andtransported to condenser 18. A fraction of the distillate is thenreturned to column 14 as reflux via conduit 19, while the remainder istransported via conduit 20 to mix with the material in conduit 8 priorto its entry into cooler 9. The entraining agent-rich layer, e.g., 11,in the decanter typically still contains concentrations of HF possiblyas high as several weight %. Optionally, instead of being sentimmediately back to column 2 via conduit 13, the entraining agent-richliquid layer, e.g., 11, in the decanter can instead first be transportedto distillation column 21 via conduit 22. Material comprising theentraining agent substantially-free of HF is removed from the column 21bottoms via conduit 23. A mixture comprising the entraining agent and HFis removed from column 21 via conduit 24 and transported to condenser25. A fraction of the distillate is then returned to column 21 as refluxvia conduit 26, while the remainder is transported via conduit 27 to mixwith the material in conduit 8 prior to its entry into cooler 9.

FIG. 2 schematically illustrates a system which can be used to performanother aspect of the inventive distillation process. A first mixturecomprising HFC-245fa and HF is supplied via conduit 27 to distillationcolumn 28. At least one liquid entraining agent is supplied via conduit29 to distillation column 28. The entraining agent may alternately bemixed in with the mixture comprising HFC-245fa and HF prior to thedistillation column and simultaneously fed in via conduit 27. Materialcomprising HFC-245fa substantially-free of HF is removed from the column28 bottoms via conduit 30. Material comprising entraining agent and HFis removed from the column 28 as distillate via conduit 31 andtransported to coolers, and from there to the decanter 33. The materialentering the decanter separates into two liquid layers, one layerentraining agent-rich, e.g., 34, the other layer HF-rich, e.g., 35. Theentraining agent-enriched layer is transported back to column 28 asreflux via conduit 36. The HF-enriched layer is transported to column 37via conduit 38. Material comprising HF substantially-free of entrainingagent is removed from column 37 via conduit 39. Material comprising theentraining agent and HF is removed from the column 37 as distillate viaconduit 40 and transported to condenser 41. A fraction of the distillateis then returned to column 37 as reflux via conduit 42, while theremainder is transported via conduit 43 to mix with the material inconduit 31 prior to its entry into cooler 32. In contrast to theconfiguration shown in FIG. 1, the configuration shown in FIG. 2 allowsfor significantly improved energy efficiency and reduced equipmentcosts.

EXAMPLES

The following Examples are provided to illustrate certain aspects of thepresent invention, and do not intend to limit the scope of the instantinvention. The following Examples employ the NRTL interaction parametersidentified earlier. In the following examples, each stage is based upona 100% operational or performance efficiency. Differing column designsand operating conditions are employed using different entraining agentsin order to maximize the performance of each distillation. The totalstages include the condenser and reboiler, with the condenser counted asstage No. 1.

Example 1

In this Example, a feed stream consisting of 75 mole % HF and 25 mole %HFC-245fa is fed to a distillation column at a rate of 100 lbs. per hourby way of conduit 44 as shown in FIG. 3. Either CFC-115, HCFC-124,HCFC-142b, CFC-114, or propane is added to this feed stream as theentraining agent prior to its entry into the distillation column, withthe flowrate shown being the total amount of each entrainer being fed tothe column. The entraining agent is added to column 47 by recycling thedecanter's organic-rich phase 55 via conduit 45 plus supplementalentraining agent added via conduit 46. Product HFC-245fa is removed asthe column bottoms via conduit 48. Distillate from column 47 is sent viaconduit 49 to the column condenser 50, where it is condensed and part ofthe condensate recycled as reflux via conduit 51. The remainingcondensed distillate is fed via conduit 52 through cooler 53 where it iscooled down to a decanter temperature of −20° C., then is fed to adecanter 54 in which it separates into two liquid layers. The decanter'slower organic-rich liquid layer, 55 is then fed back via conduit 45 andmixed with the HF and HFC-245fa feed stream and again distilled. Thedecanters upper HF-rich liquid layer, 56, may be processed by methodspreviously disclosed in this specification.

TABLE 1 HCFC- Entraining Agent CFC-115 HCFC-124 142b CFC-114 Propane #of stages 45 40 50 55 55 HFC-245fa Feed 12 15 12 35 20 Stage EntrainingAgent 12 15 12 35 20 Feed Stage Column Top −12.24 14.41 11.75 22.32 0.47Temperature (° C.) Reflux Temperature −12.54 12.50 10.10 21.79 −14.59 (°C.) Distillate −12.54 12.50 10.10 21.79 −14.59 Temperature (° C.) BaseTemperature 48.64 48.64 41.22 48.64 48.64 (° C.) HFC-245fa/HF 20.0020.00 20.00 20.00 20.00 Feed Temperature (° C.) Entraining Agent 20.0020.00 20.00 20.00 20.00 Feed Temperature (° C.) Top Pressure (psia) 44.844.8 34.8 44.8 44.8 Condenser Pressure 44.7 44.7 34.7 44.7 44.7 (psia)Base Pressure (psia) 47.7 47.7 37.7 47.7 47.7 Crude HFC-245fa 100.0100.0 100.0 100.0 100.0 Feed Rate (lbs/hr) Entraining Agent 200.0 100.0100.0 21.0 20.0 Feed Rate (lbs/hr) Distillate Rate 204.9 105.0 105.133.0 38.6 (lbs/hr) Bottoms Rate 95.1 95.0 94.9 88.0 81.4 (lbs/hr) RefluxRate (lbs/hr) 500 400 500 500 500 Reflux Ratio 2.44 3.81 4.76 15.1612.95 (molar) Condenser Duty −20671 −22214 −34409 −23669 44898 (PCU/hr)Reboiler Duty 14813 22810 29905 24449 43213 (PCU/hr) HFC-245/HF FeedHFC-245fa 0.7106 0.7106 0.7106 0.7106 0.7106 (lb-mol/hr) HF (lb-mol/hr)0.2369 0.2369 0.2369 0.2369 0.2369 Total (lb-mol/br) 0.9475 0.94750.9475 0.9475 0.9475 Distillate HFC-245fa 0.0015 0.0019 0.0025 0.05400.1036 (lb-mol/hr) HF (lb-mol/br) 0.2369 0.2369 0.2369 0.2369 0.2369Entraining Agent 1.2947 0.7327 0.9950 0.1229 0.4536 (lb-mol/hr) Total(lb-mol/hr) 1.5331 0.9715 1.2344 0.4137 0.7940 HFC-245fa 0.2053 0.25990.3303 7.2335 13.8836 Overhead (lb/br) HFC-245fa Lost in 0.2155 0.27290.3467 7.5933 14.5743 Overhead (%) Tails HFC-245fa 0.7091 0.7087 0.70820.6567 0.6070 (lb-mol/hr) HF (lb-mol/hr) 0.0000 0.0000 0.0000 0.00000.0000 Entraining Agent 0.0000 0.0000 0.0000 0.0000 0.0000 (lb-mol/hr)Total (lb-mol/hr) 0.7091 0.7087 0.7082 0.6567 0.6070 HF (ppm-molar)0.0000 0.0000 0.0000 0.0000 0.0000 Entraining Agent 0.0000 0.0044 0.00000.0006 0.0000 (ppm-molar) HFC-245fa (mol %) 100.00000 100.00000100.00000 100.00000 100.00000

Example 2

This Example demonstrates the existence of azeotropic of azeotrope-likecompositions between the binary pair mixtures consisting essentially ofHF and HFC-245fa; HF and HCFC-124; HF and CFC-114; HF and CFC-114a; HFand CFC-115; HF and HCFC-142b. To determine the relative volatility ofeach binary pair, the so-called PTx Method was used. In this procedure,for each binary, the total absolute pressure in a PTx cell of knownvolume was measured at a constant temperature for various knowncompositions. These measurements were then reduced to equilibrium vaporand liquid compositions using the NRTL equation. Samples of selectedvapor and liquid sets were obtained and analyzed to verify theirrespective compositions.

The vapor pressure measured versus the composition in the PTx cell forthe HF and HFC-245fa; HF and HCFC-124; HF and CFC-114; HF and CFC-114a;HF and CFC-115; HF and HCFC-142b systems are shown in FIGS. 4 through 9,respectively. The experimental data points are shown on each Figure assolid points, and the curve is then fitted from that data.

Referring now to FIG. 4, FIG. 4 illustrates graphically the formation ofan azeotropic or azeotrope-like composition consisting essentially of HFand HFC-245fa at a temperature of about 20° C., as indicated by mixturesof HF and HFC-245fa having a higher vapor pressure than either purecomponent. This system exhibits a maximum or peak vapor pressure at atemperature of +20° C. of about 26.7 psia, and contains about 66.1 molepercent HF and 33.9 mole percent HFC-245fa in the vapor space of thishigher pressure region. Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about84.4 mole percent HF and 15.6 mole percent HFC-245fa is formed at atemperature of about −50° C. and 0.8 psia. Based upon these findings, ithas been calculated that an azeotropic or azeotrope-like composition ofabout 44.1 mole percent HF and 55.9 mole HFC-245fa is formed at atemperature of about +130° C. and 559 psia. Accordingly, the presentinvention provides an azeotropic of azeotrope-like compositionconsisting essentially of from about 84.4 to 44.1 mole % HF and from15.6 to 55.9 mole % HFC-245fa, said composition having a boiling pointfrom about −50° C. at 0.80 psia to about +130° C. at 559 psia.

Referring now to FIG. 5, FIG. 5 illustrates graphically the formation ofan azeotropic or azeotrope-like composition consisting essentially of HFand HCFC-124 at a temperature of about 40° C., as indicated by mixturesof HF and HCFC-124 having a higher vapor pressure than either purecomponent at that temperature This system exhibits a maximum or peakpressure at +40° C. of about 107 psia, and contains about 36 molepercent HF and 64 mole percent HCFC-124 in the vapor space of thishigher pressure region. Accordingly, the present invention provides anazeotropic or azeotrope-like composition consisting essentially of about36 mole percent HF and 64 mole percent HCFC-124, having a boiling pointof about +40° C. at 107 psia. Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 42mole percent HF and 58 mole percent HCFC-124 is formed at a temperatureof about −17° C. and 13.9 psia. Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about39.0 mole percent HF and 61.0 mole HCFC-124 is formed at a temperatureof about +120° C. and 1130 psia. Accordingly, the present inventionprovides an azeotropic of azeotrope-like composition consistingessentially of from about 42 to 39 mole % HF and from 58 to 61 mole %HCFC-124, said composition having a boiling point from about −17° C. at13.9 psia to about +120° C. at 1130 psia.

Referring now to FIG. 6, FIG. 6 illustrates graphically the formation ofan azeotropic or azeotrope-like composition consisting essentially of HFand CFC-114 at a temperature of about −20° C., as indicated by mixturesof HF and CFC-114 having a higher vapor pressure than either purecomponent at that temperature This system exhibits a maximum or peakpressure at −20° C. of about 8.2 psia, and contains about 67 molepercent HF and 33 mole percent CFC-114 in the vapor space of this higherpressure region. Accordingly, the present invention provides anazeotropic or azeotrope-like composition consisting essentially of about67 mole percent HF and 33 mole percent HCFC-124, having a boiling pointof about −20° C. at 8.2 psia. Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 68mole percent HF and 32 mole percent CFC-1 14 is formed at a temperatureof about −50° C. and 1.6 psia Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 50mole percent HF and 50 mole CFC-114 is formed at a temperature of about+100° C. and 427 psia. Accordingly, the present invention provides anazeotropic of azeotrope-like composition consisting essentially of fromabout 68 to 50 mole % HF and from 32 to 50 mole % CFC-114, saidcomposition having a boiling point from about −50° C. at 1.6 psia toabout +100° C. at 427 psia.

Referring now to FIG. 7, FIG. 7 illustrates graphically the formation ofan azeotropic or azeotrope-like composition consisting essentially of HFand CFC-114a at a temperature of about +20° C., as indicated by mixturesof HF and CFC-114a having a higher vapor pressure than either purecomponent at that temperature This system exhibits a maximum or peakpressure at +20° C. of about 42 psia, and contains about 64 mole percentHF and 37 mole percent CFC-114 in the vapor space of this higherpressure region. Accordingly, the present invention provides anazeotropic or azeotrope-like composition consisting essentially of about63 mole percent HF and 37 mole percent HCFC-124, having a boiling pointof about +20° C. at 42 psia Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 65mole percent HF and 35 mole percent CFC-114a is formed at a temperatureof about −25° C. and 16.8 psia. Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 57mole percent HF and 43 mole CFC-114a is formed at a temperature of about+100° C. and 365 psia. Accordingly, the present invention provides anazeotropic of azeotrope-like composition consisting essentially of fromabout 65 to 57 mole % HF and from 35 to 43 mole % CFC-114a, saidcomposition having a boiling point from about −25° C. at 16.8 psia toabout +100° C. at 365 psia.

Referring now to FIG. 8, FIG. 8 illustrates graphically the formation ofan azeotropic or azeotrope-like composition consisting essentially of HFand CFC-115 at a temperature of about −20° C., as indicated by mixturesof HF and CFC-115 having a higher vapor pressure than either purecomponent at that temperature This system exhibits a maximum or peakpressure at −20° C. of about 35 psia, and contains about 25 mole percentHF and 75 mole percent CFC-114 in the vapor space of this higherpressure region. Accordingly, the present invention provides anazeotropic or azeotrope-like composition consisting essentially of about25 mole percent HF and 75 mole percent CFC-115, having a boiling pointof about −20° C. at 35 psiaBased upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 17mole percent HF and 83 mole percent CFC-115 is formed at a temperatureof about −60° C. and 5.5 psia. Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 24mole percent HF and 76 mole % CFC-115 is formed at a temperature ofabout +50° C. and 287 psia. Accordingly, the present invention providesan azeotropic of azeotrope-like composition consisting essentially offrom about 17 to 24 mole % HF and from 83 to 76 mole % CFC-115, saidcomposition having a boiling point from about 60° C. at 5.5 psia toabout +50° C. at 287 psia.

Referring now to FIG. 9, FIG. 9 illustrates graphically the formation ofan azeotropic or azeotrope-like composition consisting essentially of HFand HCFC-142b at a temperature of about +30° C., as indicated bymixtures of HF and HCFC-142b having a higher vapor pressure than eitherpure component at that temperature This system exhibits a maximum orpeak pressure at +30° C. of about 74 psia, and contains about 51 molepercent HF and 49 mole percent CFC-114 in the vapor space of this higherpressure region. Accordingly, the present invention provides anazeotropic or azeotrope-like composition consisting essentially of about51 mole percent HF and 49 mole percent HCFC-142b, having a boiling pointof about +30° C. at 74 psia Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 52mole percent HF and 48 mole percent HCFC-142b is formed at a temperatureof about −20° C. and 11 psia. Based upon these findings, it has beencalculated that an azeotropic or azeotrope-like composition of about 50mole percent HF and 50 mole HCFC-142b is formed at a temperature ofabout +40° C. and 92 psia. Accordingly, the present invention providesan azeotropic of azeotrope-like composition consisting essentially offrom about 52 to 50 mole % HF and from 48 to 50 mole % HCFC-142b, saidcomposition having a boiling point from about −20° C. at 10 psia toabout +40° C. at 92 psia.

It has been been calculated that an azeotropic or azeotrope-likecomposition consisting of essentially about 24 mole percent HF and 76mole percent propane is formed at a temperature of about −20° C. and 38psia. It has been calculated that an azeotropic or azeotrope-likecomposition of about 39 mole percent HF and 61 mole propane is formed ata temperature of about +60° C. and 378 psia. Accordingly, the presentinvention provides an azeotropic of azeotrope-like compositionconsisting essentially of from about 24 to 39 mole % HF and from 76 to61 mole % propane, said composition having a boiling point from about−20° C. at 38 psia to about +60° C. at 378 psia.

Example 3

This Example shows the effect of holding condensed HF and entrainingagent mixtures at various temperatures. The “Initial Mixture” column inTable 2 indicates the mole % of HF and each of the entraining agentsshown in an initial mixture, with the “initial Mixture” compositions asshown being azeotropic or azeotrope-like compositions of HF and therespective entraining agent that exist at a specific temperatures andpressures. Upon holding or bringing these mixtures as condensed liquidsto the temperatures indicated in the second column of Table 2, themixtures separate into two liquid layers.

For the purposes of the instant invention in which azeotropic orazeotrope-like initial mixtures comprising HF and an entraining agentare to be separated, Table 2 shows examples of temperatures at which thecondensed initial azeotropic or azeotrope-like mixtures forms two liquidphases, and wherein one layer is enriched in HF and the other layer isenriched in organic relative to the initial azeotropic or azeotrope-likemixture. That is to say, these temperatures are examples of where theinitial mixture separates into two layers such that the HF concentrationis higher and lower in each of the liquid layers formed respectively,when compared to the initial mixture. Generally, the lower thetemperature to which the initial mixture is cooled, the greater theefficiency of this separation. That is to say, the lower the temperatureto which the initial mixture is cooled or held, the lower the residualorganic and HF concentrations become in the HF and organic layers,respectively. By cooling azeotropic or azeotrope-like compositionssufficiently such that the mixture separates into two liquid layershaving higher and lower HF concentrations than the initial composition,the layers thus formed may then optionally be processed by methodsdisclosed in the current specification.

TABLE 2 Mole % In Initial Mole % Mole % Mixture Temp In HF Layer In Org.Layer Organic HF Organic (° C.) HF Organic HF Organic HCFC-142b 42 58+20 85 15  31 69 42 58 −20 91 9 14 86 CFC-115 32 68 +60 84 16  41 59 2773 −20 96 4  6 93 CFC-114 81 19 +100  97 3 14 86 90 10 +20 99 1  2 97HCFC-124 43 57 −10 75 25  35 65

Example 4

This Example shows the results of PTx measurements and NRTL calculationsfor azeotropic or azeotrope-like compositions found formed between HFand various compounds. We have found effective entraining agents forseparating HF from HFC-245fa to be those compounds forming low-boilingazeotropic or azeotrope-like compositions with HF, which saidcompositions have higher maximum or peak pressures than that ofHF/HFC-245fa azeotropic or azeotrope-like compositions when saidazeotropic or azeotrope-like compositions are compared at the sametemperature.

Table 3 compares the maximum or peak pressure of azeotropic orazeotrope-like compositions formed between HF and HFC-245fa with thoseformed between HF and a variety of other hydrocarbon, hydrofluorocarbon,hydrochlorocarbon, hydrochlorofluorocarbon, and fluorocarbon compounds.“Normal boiling point” refers to the normal or atmospheric boiling pointof HFC-245fa or of the other hydrocarbon, hydrofluorocarbon,hydrochlorocarbon, hydrochlorofluorocarbon, hydrochlorocarbon orfluorocarbon compounds shown. The maximum or peak pressure of theazeotropic or azeotrope-like composition formed between HF and each ofHFC-245fa, the hydrocarbon, hydrofluorocarbon, hydrochlorocarbon,hydrochlorofluorocarbon, hydrochlorocarbon or fluorocarbon compoundindicated, at each of 0° C. and 50° C. as examples, is shown forcomparison. We have found effective entraining agents for separating HFand HFC-245fa by distillation according to the instant invention to bethose forming azeotropic or azeotrope-like compositions having peak ormaximum pressures higher or greater than that of azeotropic orazeotrope-like compositions of HF and HFC-245fa when the pressures ofthe azeotropic or azeotrope-like compositions are compared at the sametemperature.

TABLE 3 Peak Pressure of Low-Boiling Normal Azeotrope with HF Boiling(PSIA) Point (° C.) At 0° C. at 50° C. HFC-245fa  15 +12 +73 Thefollowing are entraining agents of the present process, as their HF-azeotropes have higher peak pressures than the HF/HFC-245fa azeotrope atthe same temperature. Propane −42 +75 +295 n-Butane −1 +23 +122 CFC-12(CCl₂F₂) −30 +52 +215 CFC-114 (CClF₂CClF₂) +4 +19 +106 CFC-114a(CClFCF₃) +3 +20 +106 CFC-115 (CClF₂CF₃) −39 +71 +295 CFC-217ba(CF₃CClFCF₃) −3 +22 +118 HCFC-21 (CHFCl₂) +9 +16 +92 HCFC-22 (CHClF₂)−41 +75 +285 HCFC-124 (CF₃CHClF) −12 +28 +141 HCFC-124a (CHF₂CClF₂) −10+28 +141 HCFC-133a (CClH₂CF₃) +6 +17 +92 HCFC-142b (CClF₂CH₃) −9 +26+127 PFC-218 (CF₃CF₂CF₃) −37 +68 — Perfluorocyclobutane −6 +25 +130Perfluoro-n-butane −2 +22 +120 The following are not entraining agentsin the present invention as their HF azeotropes have lower peakpressures than the HF/HFC-245fa azeotrope at the same temperature.CFC-112 (CCl₂FCCl₂F) +93 +7 +43 CFC-113 (CFCl₂CCl₂F) +48 +8 +55 HCFC-123(CHCl₂CF₃) +28 +12 +68 HCFC-141b (CCl₂FCH₃) +32 +11 +64 HCC-150a(CHCl₂CH₃) +57 +8 +50 HCFC-151a (CHClFCH₃) +16 +12 +72 CFC-216aa(CF₃CClFCClF₂) +33 +10 +64 Methylene Chloride (CH₂Cl₂) +40 +9 +58n-Hexane +69 +6 +48 n-Pentane +36 +11 +66

What is claimed is:
 1. A process for separating1,1,1,3,3-pentafluoropropane (HFC-245fa) from hydrogen fluoride (HF),comprising: contacting a first mixture comprising1,1,1,3,3-pentafluoropropane (HFC-245fa) and hydrogen fluoride (HF) withan entraining agent selected from the group consisting of hydrocarbons,chlorofluorocarbons, hydrochlorofluorocarbons and fluorocarbons, whereinsaid entraining agent has a normal boiling point of from about −50° C.to about 10° C., to form a second mixture, distilling the second mixtureand thereby separating the 1,1,1,3,3-pentafluoropropane (HFC-245fa) fromhydrogen fluoride (HF) and entraining agent, and recovering1,1,1,3,3-pentafluoropropane (HFC-245fa).
 2. The process of claim 1wherein the first mixture comprises an azeotrope of1,1,1,3,3-pentafluoropropane (HFC-245fa) and hydrogen fluoride (HF). 3.The process of claim 1 wherein the entraining agent is selected from thegroup consisting of chloro-1,1,1,2-tetrafluoroethane (HCFC-124),chloro-1,1,2,2-tetrafluoroethane (HCFC-124a),dichloro-1,1,2,2-tetrafluoroethane (CFC-114),dichloro-1,1,1,2-tetrafluoroethane (CFC-114a),1-chloro-1,1-difluoroethane (HCFC-142b), chloropentafluoroethane(CFC-115), propane, n-butane, dichlorodifluoromethane (CFC-12),2-chloro-1,1,1,2,3,3,3-heptafluoropropane (CFC-217ba),dichlorofluoromethane (HCFC-21), chlorodifluoromethane (HCFC-22),2-chloro-1,1,1-trifluoroethane (HCFC-133a), octafluoropropane (PFC-218),perfluorocyclobutane and perfluoro-n-butane.
 4. The process of claim 1wherein the recovered 1,1,1,3,3-pentafluoropropane (HFC-245fa) issubstantially-free of hydrogen fluoride (HF).
 5. The process of claim 1wherein the recovered 1,1,1,3,3-pentafluoropropane (HFC-245fa) containsless than about 1 part-per-million-by-weight (ppmw) hydrogen fluoride(HF).
 6. The process of claim 1 wherein the recovered1,1,1,3,3-pentafluoropropane (HFC-245fa) contains less than about 100parts-per-billion-by-weight (ppbw) hydrogen fluoride (HF).
 7. Theprocess of claim 1 further comprising: recovering an azeotropic orazeotrope-like third mixture comprising HF and entraining agent asdistillation column overhead from said distilling step, cooling andthereby phase-separating the third mixture into a fourth mixturecomprising an HF-enriched phase and a fifth mixture comprising anentraining agent enriched phase, and recycling the fifth mixture back tosaid contacting step.
 8. The process of claim 1 further comprising:recovering an azeotropic or azeotrope-like third mixture comprising HFand entraining agent as distillation column overhead from saiddistilling step, cooling and thereby phase-separating the third mixtureinto a fourth mixture comprising an HF-enriched phase and a fifthmixture comprising an entraining agent enriched phase, distilling thefourth and/or fifth mixtures under conditions sufficient to form anazeotrope or azeotrope-like sixth mixture comprising HF and entrainingagent as distillation column overhead, recovering a seventh mixturecomprising HF or entraining agent as distillation bottoms from saiddistilling step of the fourth and/or fifth mixtures, recycling the sixthmixture to said cooling step, and recycling the seventh mixture to saiddistilling step of the fourth and/or fifth mixtures.